Previous research indicates that the amplitude of the overt (whole body) startle reaction is, in part, determined by the acoustical and visual events that precede presentation of the startle eliciting stimulus. Proposed research will examine the effects of various antecedent visual and acoustic stimuli on the startle reactions of rats and pigeons. The research will also examine the effects of various antecedent acoustic signals on the eyeblink elicited by a tap to the glabella in humans. This assessment of the manner in which eyeblinks vary with antecedent signal intensity and frequency is designed to provide information for the development of a new technique for assessing hearing in audiologically impaired children and adults.